In various semiconductor devices, it is necessary to reduce a contact resistance between a semiconductor and a metal semiconductor compound electrode. For example, in order to reduce the contact resistance, there is a method of forming a high-concentration dopant layer near an interface between the semiconductor and the metal semiconductor compound electrode by ion implantation or epitaxial growth.
For example, in a power MOSFET (Metal Oxide Semiconductor Field Effect Transistor) that is of a semiconductor switch driven at a high breakdown voltage, it is necessary to maintain a carrier concentration at a low level in order to increase an breakdown voltage of the device.
In the method of forming the high-concentration dopant layer, such as ion implantation or epitaxial growth, the impurity diffuses in a low-concentration substrate by a subsequent process, which may results in a decrease of the breakdown voltage of the device. And also, the formation of the high-concentration impurity layer by the ion implantation or the epitaxial growth causes an increase of process cost of the device.
There is well known a method, in which a non-dopant impurity such as sulfur is introduced by the ion implantation to lower a Schottky barrier height and the contact resistance between the semiconductor and the metal semiconductor compound electrode is reduced.